SAFOD Insights into the “Earthquake Machine”

Scientists working with the San Andreas Fault Observatory at Depth will be presenting two talks at AGU this week, detailing new insights to how earthquakes start. Earlier this summer, the SAFOD borehole completed a major goal of drilling through the active fault zone along the San Andreas Fault near Parkfield.

One of the interesting discoveries along the fault involves nonvolcanic tremors that seem to correlate well with actual earthquakes that happen at later point in time.

From 2000 to 2003, before SAFOD drilling began, researchers from the University of California-Berkeley recorded 110 nonvolcanic tremor events along the San Andreas Fault near Parkfield. Their data showed a remarkable correlation between the frequency of tremor events and the subsequent earthquakes. The scientists discovered that an increase or decrease in the number of tremor events over a certain period of time would usually be matched by a similar increase or decrease in the number of microearthquakes (magnitude 2.1 or smaller) several weeks later, suggesting a possible causal relationship.